Analysis and design of a novel noncontacting waveguide backshort

A new noncontacting waveguide backshort has recently been developed for millimeter- and submillimeter-wave frequencies. The design consists of a metal bar with rectangular holes cut into it, which is covered with a dielectric layer to form a snug fit with the broadwalls of a waveguide. It is mechanically rugged and can be readily fabricated for frequencies from 1-1000 GHz. This paper presents a technique for the theoretical characterization of the backshort, using an approach that combines the mode-matching method and a set of coupled space-domain integral equations. The convergence characteristics of the analysis are included, along with a set of general design guidelines     

A 100-GHz-band heterodyne sis receiver for the trao telescope

A 100-GHz-band Superconductor-Insulator-Superconductor (SIS) receiver has been developed for radio astronomy. The mixer used in this receiver has no mechanical tuning elements, such as a backshort or an E-plane tuner. The SIS junction consists of an array of four Nb/Al-AIOx/Nb junctions in series. The quasi-optic system for this receiver has been designed by frequency-independent matching method. The average DSB receiver noise temperature measured in the frequency range from 85 to 115 GHz is 40 K. The receiver is being successfully operated at the Taeduk Radio Astronomy Observatory in Korea.     

Low-noise 320?360 GHz cryogenically cooled waveguide Schottky diode mixer

Construction details and results of noise measurements on a cryogenically cooled Schottky diode mixer for the 320?360 GHz range are given. Critical mixer parts are electro-formed or machined on a precision lathe. The system double-sideband noise temperature is close to 400 K over a 30 GHz range with a lowest temperature of 385 K at 335 GHz. The mixer uses a tunable contacting backshort and has a total RF/IF double-sideband conversion loss of about 6dB, including input lens and diplexer losses. Corrected for input losses and second-stage contribution, a mixer double-sideband noise temperature of 271 K has been calculated at 335 GHz. This mixer has shown reliable and reproducible performance during five cooldowns to 15 K.     

Quality and performance of tunable waveguide backshorts

A technique is presented for determining the quality of tunable short circuits used as backshorts in waveguide mixers. A backshort, suitable for use in a reduced height 345 GHz Schottky mixer block, has been fabricated in a novel manner and the VSWR determined, using the authors' technique, to be >90 at room temperature.<>     

Low-noise SIS heterodyne receiver at 230 GHz

A 230 GHz laboratory receiver has been built using a superconductor-insulator-superconductor (SIS) junction as the mixing element. The junction is mounted in 4:1 reduced-height waveguide, terminated at one end with a circular adjustable backshort. Recent results indicate a receiver noise temperature of TR ? 120 K (DSB).     

The effect of mixer mount loss on the performance of SIS receivers

Tucker's quantum theory of mixing (in the 3-port approximation) is employed with Eisenhart and Khan's equivalent circuit for a junction mounted in waveguide to predict the gain of an SIS mixer as a function of guide impedance, series inductance, junction capacitance, IF load impedance and backshort loos. The improvements which will result from optimisation of these parameters are quantified. It is shown that for optimum performance a backshort VSWR>100 is required, which is hard to realise at high frequencies     

Planar multimode detector arrays for infrared and millimeter-wave applications

A new type of detector array is described. By means of a suitably designed metallic network, many detector elements (each individually small compared to wavelength) are assembled into an impedance-matched termination for radiation incident normally on the plane of the device. Residual reactance is tuned out by means of a movable backshort. An array of 400 bismuth-film microbolometers with a total area of 1 cm²has been tested at 215 GHz. A coupling efficiency of approximately 60 percent was observed. The detector has aD*of4 times 10^{8}cm . Hz^1/2/W at room temperature with response time on the order of2 times 10^{-7}s. Similar arrays of Schottky and SIS diodes can probably be constructed.     

A 345 GHZ heterodyne receiver for the James Clerk Maxwell Telescope

In this paper we describe the design and performance of a low-noise 345 GHz heterodyne receiver. The mixer uses a lead alloy SIS tunnel junction mounted in reduced height rectangular waveguide and is tuned with a single backshort. Local oscillator power is provided by a broad-band Gunn oscillator which drives a frequency quadrupler. The heterodyne performance has been verified in the laboratory using a gas absorption cell. In November 1991 this receiver was successfully commissioned and by direct comparison with a Schottky diode receiver we confirm a best receiver noise temperature of 150K (DSB) at 355 GHz and a tuning range of 300 to 380 GHz. The receiver is now available as a JCMT facility instrument.     

Full-wave analysis of waveguide-to-microstrip transitions for millimeter wave applications

A “full-wave” solution is presented for the waveguide to microstrip transition. The exact Green's function of the transition is used in a moment method procedure. The behavior of the microstrip transition to a rectangular waveguide is studied with respect to the critical dimensions of the microstrip width, length and backshort location. The convergence characteristics of the full wave analysis method are investigated, along with the current distribution and the input impedance. Results given for the return loss is compared with measurements.     

An experimental submillimetre heterodyne array receiver

We describe an experimental array receiver intended for radioastronomical observations of the J=3→2 line of carbon monoxide. It consists of six indium antimonide mixers cooled to ～2K in a pumped helium cryostat, with rectangular feed horns arranged on a 3×2 grid at the f/9 focus of the UK Infrared Telescope (UKIRT). Each detector is mounted in a length of fundamental mode waveguide and has an independently tunable backshort. Local oscillator power is provided by a frequency tripler pumped by a klystron, and is coupled to the array via a “lossless” quasi-optical coupler which is described in detail. The beam patterns and performance of the coupler have been measured and are in good agreement with theory.     

分形开槽减缩微带天线RCS

分形由于其独特的结构及性能早已在天线的设计中有所应用,但较少地应用于天线雷达散射截面减缩。本文首次将分形思想应用到开槽微带天线中。设计了一副分形开槽微带天线,与常规微带天线相比,在辐射性能降低不多的同时较好地实现了整个频带RCS减缩。     

一种Ka波段基片集成波导功率合成器的设计

笔者设计了一种结构简单,容易制造的基片集成波导功率分配器／合成器,该分配器／合成器采用渐变微带线——波导的过渡结构,并且厚度只有1．254mm。通过HFSS仿真软件,设计了一个中心频率为35GHz的Ka频段的功率分配器。仿真结果显示此种结构具有极低的插入损耗和较低的回波损耗。     

ASUR-an airborne SIS receiver for atmospheric measurements of tracegases at 625 to 760 GHz

A heterodyne receiver making use of a SIS waveguide mixer with integrated horn and single backshort tuner has been built. It has been used for a series of airborne measurements of atmospheric trace gases, such as HCl and ClO, above northern Europe during the winter of 1993 and 1994. The receiver is suitable for measurements in the range of 625-760 GHz and shows stable operation in the airplane together with high sensitivity. Best achieved noise temperatures are T_DSB=310 K at 708 GHz in the laboratory and T_SSB=1500 K at 625 GHz for the complete system in the airplane     

An Efficient 200-290-GHz Frequency Tripler Incorporating a Novel Stripline Structure

This paper describes a broadly tuneable frequency tripler which can provide more than 2-mW output power at any frequency between 200 and 290 GHz. It is derived from an earlier narrow-band prototype design, with the major improvements being the use of a new low-pass filter design implemented using a novel suspended substrate stripline structure, an optimized waveguide transformer, and a lower loss contacting output backshort.     

A novel noncontacting waveguide backshort for submillimeter wave frequencies

A novel noncontacting waveguide backshort has been developed for millimeter wave and submillimeter wave frequencies. It employs a metallic bar with rectangular or circular holes. The size and spacing of the holes are adjusted to provide a periodic variation of the guide impedance on the correct length scale to give a large reflection of rf power. This design is mechanically rugged and can be readily fabricated for high submillimeter wave frequencies where conventional backshorts are difficult or impossible to fabricate. Model experiments have been performed at 4 GHz – 6 GHz to empirically optimize the design parameters. Values of reflected power greater than 95% over a 30% bandwidth have been achieved. A specific design is presented which has also been successfully scaled to WR-10 band (75 GHz – 110 GHz). A theoretical analysis is compared to the experiments and found to agree well with the measured data.     

Low-Profile Air-Filled Antenna for Next Generation Wireless Systems

In this study, a novel design of insensitive antenna with improved radiation performance is designed and investigated. The antenna exhibits excellent performance in terms of impedance-matching, radiation and total efficiencies, even though it is designed and fabricated using high loss substrate (FR) with compact dimension. An L-shaped metal-ring resonator has been used as a main resonator of the antenna to operate at 18.5 GHz. In order to improve the antenna performance, a part of substrate with L-shaped configuration has been removed and a metal ring structure is inserted. By using this technique, we can improve the efficiency characteristic of the antenna and eliminate the effect of high-loss FR-4 substrate. The center frequency of the designed antenna can be controlled by adjusting the values of the antenna parameters. Since the main substrate of the resonator is the air, the antenna is insensitive for different types of antenna substrates. It has the return loss characteristic less than ?10 dB in the frequency range of 17.5–19.5 GHz (more than 10% fractional bandwidth). The antenna has a very compact size with good radiation behavior and could be used in phased array antennas for next generation systems.     

A 345GHz SIS receiver for radio astronomy

A 345GHz superconductor insulator superconductor (SIS) tunnel junction receiver utilizing a full height rectangular waveguide mixer with two tuning elements, i.e. an E-plane and backshort tuner, has been constructed and installed on the Caltech Submillimeter Observatory 10m antenna on Mauna Kea, Hawaii. The receiver exhibits a best double side-band noise temperature response of 150K±20K (averaged over a 500 MHz IF bandwidth centered at 1.5GHz) at a design center frequency of 345GHz and at an ambient temperature of approximately 3.8K. Additional measurements show that the receiver has an excellent response at selected points within an RF input range of 280 to 363GHz.     

8mm基片集成波导环行器的研究与设计

提出了一种设计毫米波环行器的新方式,以进一步缩小器件体积并维持良好性能。具体方案为:通过SIW使器件具有小体积和高功率;通过弧形SIW将传统的Y字型环行器变为准T字型环行器;通过渐变器将SIW过渡到50Ω的标准微带线上,该渐变器可以内嵌到SIW内使器件体积更小。8mm环行器采用高频层压板和圆柱铁氧体进行设计,并通过高频电磁场仿真软件(HFSS)进行验证,得到工作频带内插入损耗小于0.2dB,隔离度大于20dB,回波损耗大于25dB,驻波小于1.2的结果。按设计得到的产品,其性能测试结果和仿真结果基本吻合,但工作频率有所下降。     

Efficient generation of guided millimeter-wave power by photomixing

A 70-GHz bandwidth commercial photodiode has been coupled to W-band waveguide and used as a photomixing source from 75 to 170 GHz. Maximum power conversion efficiency of 1.8% was obtained at 75 GHz, where an optical input of +10 dBm yielded a nonsaturated millimeter-wave (mm-wave) power of -7.5 dBm. Optimizing the photomixer backshort tuning at individual frequencies showed that the mm-wave power decreased with frequency to a level of -30 dBm at 170 GHz. Fixed tuning allowed the generation of power across the full waveguide band from 75 to 110 GHz, with a variation within 5 dB across the majority of the band     

Design of Tip Loss Profile on Support Rod for a Helix TWT

This paper describes the design of tip loss profile on support rod for a high gain, high efficiency helix TWT. The tip loss profile at sever ends for the input and the output section of the helix slow wave structure has been designed for return loss at severs ends better than -20 dB. The experimental results have been carried out in the input and the output section of the helix assemblies for the high gain helix TWT to find the return loss in the region of carbon coated tip loss on the support rods. The experimental result has been compared with the simulated performance for the return loss at the sever ends. The design of tip loss profile on the support rod for helix TWT has been carried out in real situation using Ansoft HFSS. A good agreement has been found in the simulated and experimental results.